The only way you should be able to void your warranty is if a part failed, and the manufacturer could show that it was caused by the lift you installed.
I would suggest you do the dual battery set up before you add any more light, or that winch, then since most of you driving is camping, and expedition, I would go with the fridge you will use it more, from there you are on your own .
There is one for sale in the paper, I am in Jerome Idaho. Times news, it says 76 Land Cruiser fj-40 dual tanks small block Chevy, phone 731-3153. I am not affiliated.